Summary of Quarterly Operating Results and Comprehensive Income (Loss) (Unaudited) (Quarterly Results) (Details 1) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Revenues
Operating Revenues	$ 787,011	$ 716,982	$ 652,871	$ 732,257	$ 763,478	$ 738,820	$ 737,602	$ 692,199	$ 2,889,121	$ 2,932,099	$ 2,695,966
Operating Costs and Expenses
Selling, general and administrative	209,202	166,207	162,840	177,152	192,494	178,182	172,297	174,686	715,401	717,659	750,926
Depreciation of property, plant and equipment	16,159	18,481	22,913	16,704	16,495	15,351	13,884	13,523	74,257	59,253	56,722
Amortization of intangible assets	14,138	14,150	14,327	14,165	13,731	13,572	12,880	13,060	56,780	53,243	47,414
Impairment of goodwill and other long-lived assets	342	1,916	11,511	16,401	8,087	372	693	0	30,170	9,152	8,109
Costs and Expenses	740,810	676,738	646,994	724,172	733,166	722,552	679,639	652,196	2,788,714	2,787,553	2,449,805
Income from Operations	46,201	40,244	5,877	8,085	30,312	16,268	57,963	40,003	100,407	144,546	246,161
Equity in earnings (losses) of affiliates, net	2,937	4,092	1,182	(1,547)	3,835	4,683	1,467	1,679	6,664	11,664	14,473
Interest income	876	890	954	1,151	1,398	1,474	1,579	1,700	3,871	6,151	5,353
Interest expense	(16,008)	(7,247)	(7,377)	(7,678)	(7,192)	(6,776)	(8,386)	(7,425)	(38,310)	(29,779)	(37,902)
Non-operating pension and postretirement benefit income, net	18,287	10,489	12,136	18,403	111,061	19,556	12,253	19,928	59,315	162,798	120,541
(Loss) gain on marketable equity securities, net	61,926	59,364	39,890	(100,393)	49,407	17,404	7,791	24,066	60,787	98,668	(15,843)
Other income (expense), net	203,524	222	8,100	2,688	(3,704)	5,556	1,228	29,351	214,534	32,431	2,103
Income (Loss) Before Income Taxes	317,743	108,054	60,762	(79,291)	185,117	58,165	73,895	109,302	407,268	426,479	323,508
Provision for (Benefit From) Income Taxes	80,800	30,000	41,900	(45,400)	39,100	15,200	16,700	27,600	107,300	98,600	52,100
Net (Loss) Income	236,943	78,054	18,862	(33,891)	146,017	42,965	57,195	81,702	299,968	327,879	271,408
Net Loss (Income) Attributable to Noncontrolling Interests	198	(439)	(8)	646	(136)	180	(114)	46	397	(24)	(202)
Net (Loss) Income Attributable to Graham Holdings Company Common Stockholders	237,141	77,615	18,854	(33,245)	145,881	43,145	57,081	81,748	300,365	327,855	271,206
Quarterly Comprehensive (Loss) Income	$ 536,772	$ 98,878	$ 35,922	$ (71,188)	$ 267,238	$ 25,059	$ 44,986	$ 90,038	$ 600,384	$ 427,321	$ 134,369
Per Share Information Attributable to Graham Holdings Company Common Stockholders
Basic net income (loss) per common share (in usd per share)	$ 47.45	$ 15.25	$ 3.61	$ (6.32)	$ 27.45	$ 8.12	$ 10.74	$ 15.38	$ 58.30	$ 61.70	$ 50.55
Basic average number of common shares outstanding (in shares)	4,970	5,060	5,196	5,274	5,284	5,285	5,285	5,284	5,124	5,285	5,333
Diluted net income per common share (in usd per share)	$ 47.34	$ 15.22	$ 3.60	$ (6.32)	$ 27.25	$ 8.05	$ 10.65	$ 15.26	$ 58.13	$ 61.21	$ 50.20
Diluted average number of common shares outstanding (in shares)	4,982	5,072	5,201	5,274	5,324	5,329	5,329	5,326	5,139	5,327	5,370
Services [Member]
Operating Revenues
Operating Revenues	$ 563,597	$ 492,399	$ 483,595	$ 516,637	$ 532,452	$ 522,195	$ 539,644	$ 516,744	$ 2,056,228	$ 2,111,035	$ 2,114,777
Operating Costs and Expenses
Cost of services and goods	309,364	298,250	298,578	333,049	325,222	345,476	326,756	318,474	1,239,241	1,315,928	1,172,855
Goods [Member]
Operating Revenues
Operating Revenues	223,414	224,583	169,276	215,620	231,026	216,625	197,958	175,455	832,893	821,064	581,189
Operating Costs and Expenses
Cost of services and goods	$ 191,605	$ 177,734	$ 136,825	$ 166,701	$ 177,137	$ 169,599	$ 153,129	$ 132,453	$ 672,865	$ 632,318	$ 413,779